Precision micro-holes in nozzles of fuel-injection systems are usually introduced with the aid of erosion methods. Using this technology, it is currently possible to produce minimal diameters of approximately 120 μm in large-scale production. Furthermore, laser drilling also allows the production of precision holes having diameters of less than 120 μm, but this has not yet been introduced as large-scale method.
In the fuel-injection field, there is increasing demand for conical holes to the effect that a fuel-outlet orifice have a smaller diameter than a fuel-intake orifice. Such precision micro-holes are already utilized in systems for diesel fuels (direct injection) or for gasoline (manifold and direct injection).
German Patent No. DE 199 055 71 describes a laser-drilling method in which a laser beam executes a wobbling motion relative to a workpiece. This has the effect that a cone-shaped shell surface is traversed inside the workpiece. The polarization plane of the laser beam is rotated in synchrony with the wobbling motion.
German Patent Application No. DE 100 548 53 describes a method for introducing a micro-hole in a workpiece by means of a laser beam. In this case, the focus of the laser beam is moved continually along a circular path which is concentric with respect to the hole axis, the laser beam being composed of a succession of short laser pulses.
In all current drilling methods, the produced bore must be subjected to follow-up treatment by hydro-erosive (HE) rounding. In fuel injection systems, for instance, this is done primarily to round the edge of the fuel intake (in addition to improving the surface of the bore wall and reducing the variance among the hydraulic flow rates of the individual bore holes of a nozzle). This results in a considerable reduction of the flow resistance at this point and also reduces undesired cavitation manifestations.
An additional considerable improvement in this direction is achieved by the combination of conicalness and distinct HE-rounding.